The inorganic molecule nitric acid has the formula HNO3. It's a mineral acid that's quite corrosive. Although the chemical is colourless, older samples have a yellow hue due to breakdown into nitrogen oxides. In water, the majority of commercially available Concentrated Nitric Acid has a concentration of 68 percent. Fumigating nitric acid is defined as a solution that contains more than 86 percent HNO3. Fumigating nitric acid is classified as red fuming nitric acid at concentrations above 86 percent, or white fuming nitric acid at concentrations above 95 percent, depending on the amount of nitrogen dioxide present.